1. Field of the Invention
This invention relates to photographic cameras, and more particularly to a camera having an automatic exposure control circuit with an electrical power supply transfer system rendering it possible to energize the exposure control circuit from either of two batteries, one of which is provided in the camera, and the other of which is provided in an accessory equipment such as a motor drive unit, as is selected in automatic response to the lowering of the voltage of the camera's battery below a satisfactory operating level.
2. Description of the Prior Art
The conventional electrical power systems for cameras having automatic exposure control apparatus have generally been designed to operate with a single battery of small size with small capacity. When the battery voltage has fallen below a satisfactory operating level, or when the operator has forgotten to have a battery mounted in his camera, the exposure control apparatus is maintained unintentionally de-energized. In the case of a camera having an electrically timed shutter, therefore, the actuation of a shutter release does not result in operation of a shutter electromagnet, thereby the shutter is caused to remain in either open or closed position, thus enabling the operator to make an exposure. In the case of a camera provided with electromagnetically operated actuating means for operation of the various internal mechanisms thereof, when the battery voltage is lowered from the satisfactory operating level, or when no battery is mounted in the camera, the internal mechanisms can not work to enable the operator to make an exposure. Although the camera can be rendered normally operative by replacing the old battery by new one, when it happens that the operator has no new batteries at hand, no further continuance of exposures can be made.
An object of the present invention is to overcome the above mentioned drawbacks of the conventional electrical power system, and to provide an electrical power supply transfer or changeover system for a photographic camera having electrically operated control means including automatic exposure control means as established in combination with an accessory equipment attached to the camera, so that when the voltage of the camera's battery has fallen below a satisfactory operating level, or when no battery is mounted as the operator has forgotten to do, the electrical power system is energized from the battery of the accessory euipment.
Another object is to detect the actual voltage of the electrical power source provided in the camera to produce an actuating signal by which a transfer switch is operated so as to shift the connection of the power system from the electrical power source of the camera to an electrical power source provided in an accessory equipment attached to the camera.